As is known, currently available electric chucks for machine tools are constituted by an electric motor, generally of asynchronous type, coupled to a chuck capable of holding the rotating tool to be driven. Generally, the chuck is provided with a device for gripping and releasing the tool in such a way as to be able to exchange one rotating tool for another rapidly.
The electric rotor of the electric chuck normally comprises a stator of tubular form extending coaxially of the longitudinal axis of the motor; a rotor of substantially cylindrical form mounted rotatably within this stator to turn about the longitudinal axis of the motor; and a protective casing containing the stator and the rotor. In particular, the stator is fixed to the interior of the casing whilst the rotor is maintained within the stator, coaxial with the longitudinal axis of the motor, by means of rolling element bearings interposed between the rotor and the casing.
The electric motor is, moreover, provided with a cooling fan for producing a stream of air, which by flowing over the outer surface of the casing of the motor carries away the heat produced by the rotor and the stator during normal operation.
However, the cooling of the electric motor achieved by this cooling fan is not particularly efficient and thus constrains the producers of electric chucks to limit the performance of their products. Neglecting the mechanical losses the power which can be delivered by an electric chuck is in fact equal to the power available from the electric motor which is, in turn, limited by the quantity of heat which can be dissipated per unit of time through the casing of the electric motor without exceeding the operating temperature limit.
In particular, the parameter which strongly influences the power which can be delivered by the electric motor of the electric chuck is the maximum quantity of heat which can be dissipated per unit of time from the rotor, this latter being in fact the element of the electric motor which has the greatest difficulty in dissipating the heat produced.